This invention relates to designs for cams to operate magnetically balanced fingers of a peristaltic pump. At present peristaltic pumps find use in medical settings to add nutrients to blood, to force blood through filters to clean it as in dialysis, or to move blood through the body and lungs during open heart surgery. They are advantageous in these situations since the pump elements do not contact the pumped fluid, eliminating any possibility of contamination. Additionally the pumping action may be gentle enough that blood cells are not damaged. Further uses include pumping aggressive chemicals, high solids slurries and other materials where isolation of the product from the environment, and the environment from the product, are critical. As the operation of such a pump can be critical for life support, they are generally provided with battery backup. The efficiency of the device thus becomes an important parameter since the length of time it can remain in operation while on battery power is limited by its efficiency.
A common arrangement for the operation of a peristaltic pump is shown in the prior art of FIG. 1 (100 is a front view and 101 is a lateral view), wherein a plurality of fingers 104 press the feed tube 103 against a substrate 105 by means of a cam 102. Neighboring fingers are operated in sequence such that a squeezing or ‘peristaltic’ motion operates along the length of the tube, forcing the contents of the tube in one direction. By adjusting the speed of rotation of the cams, the speed of pumping can be adjusted.
In U.S. Pat. No. 4,725,205 a mechanically compensated cam for use in a peristaltic pump is disclosed. The system described uses specially designed cams that reduce the maximum force applied between fingers 104 and tube 103 by means of a compliant spring. In this manner problems of jamming due to poor alignment or out-of-tolerance tubes are eliminated. This system while effective and simple involves a certain amount of wasted energy as will be described below. Furthermore, being based on an eccentric circle, the fingers follow a trajectory sinusoidal in nature, which limits the volume pumped per camshaft revolution. Varying the trajectory from that of a sinusoid would offer the benefit of fixing the duration during which the tube is shut off, allowing for an increase in the volume pumped per revolution.
Thus a design and method for the cam of a peristaltic pump allowing a tailored finger trajectory that reduces the probability of jamming in out-of-tolerance tubes, as well as allowing increased volume per rotation and subsequent enhanced energy savings is a long felt need.